ABSTRACT
Abstract Carbon tetrachloride (C C I4 ) and its dechlorination products are toxic and/or carcinogenic in mammals. Thus, their environmental fate is of concern to both environmental scientists and government regulators. A unique C C I4 dechlorination mechanism has been discovered in cultures of iron-limited Pseudomonas stutzeri strain KC. This mechanism is characterized by extensive hydrolysis to give CO2 as a major product, with low or undetectable levels of chloroform. A low-molecular-weight metal chelator promotes this route of C C I4 decomposition. That agent is pyridine2,6-bis(thiocarboxy lie acid) (pdtc). Although pdtc synthesis is regulated by iron stress, preliminary results from 59Fe uptake experiments suggest that pdtc is not the bacterium’s primary siderophore. Unlike other siderophores, pdtc chelates copper(II), cobalt(III), and iron(III) with similar, very high affinity (Kd = 1034). The affinity decreases dramatically (1012) when iron(III) is reduced to iron(II), suggesting that pdtc functions as a siderophore towards iron in P. stutzeri but is not required for growth of the bacterium in low-iron media. Pdtc chelates many transition metals, some heavy metals, and also some lanthanides. Pdtc has antimicrobial activity, and this may be its main physiological function in nature. Pdtc is produced by P stutzeri during both anaerobic and aerobic growth. P. stutzeri is a classic facultative anaerobic bacterium (denitrifier) and can be used for C C I4 degradation in either the presence or absence of oxygen. The reaction of pdtc with C C I4 does not require oxygen since it forms thiophosgene and this intermediate hydrolyzes to CO2, H2S, and HC1. Current research is elucidating the genetic basis of pdtc biosynthesis and resistance to it by its producers. This knowledge should allow the ultimate use of pdtc or pdtc-producing microorganisms for in situ bioremediation of C C I4 and/ or heavy metals and radionuclides in locations such as anaerobic aquifers.
